1. Field of the Invention
The present invention is directed generally to plasma processing chambers and, more particularly, to inductively coupled processing chambers.
2. Description of the Background
Plasma processing chambers are used in a number of different industries. For example, plasma processing chambers are used in the fabrication of integrated circuits, for coating medical devices, and for coating mirrors. Plasma processing chambers may be either inductively coupled or capacitively coupled. In the capacitively coupled systems, electrodes comprised of parallel plates are energized to produce the plasma. In the inductively coupled systems, an inductive coil is energized to produce the plasma. In both systems, varying the parameters of the mechanism used to generate the plasma provides some ability to control the characteristics of the generated plasma.
For example, in inductively coupled systems, the coil has a time varying radio frequency voltage impressed thereupon. The electron heating zone in the inductively coupled plasma is shaped like a torroid whose diameter is affected by the coil geometry. The value of the capacitor between the coil and ground may also effect the size and location of the electron heating zone.
In the semiconductor industry, a plasma chamber may be used to carry out a variety of processes such as etching, deposition, sputtering, and annealing. Many of those processes leave contaminant depositions throughout the processing chamber. Such contaminants may adversely impact the process step being performed which, in turn, can adversely impact device yield. The adverse impact on device yield becomes more pronounced as device size decreases.
Another problem is the wear out of the dielectric parts (the plate) within the processing chamber. Wear out of the plate is a particular problem when the chamber is used for etching. For example, an etching process can result in the deposition of a polymer on the plate. A cleaning step is required to remove that polymer. The efficacy of the cleaning step depends on a number of parameters, one of which is the value of the capacitive coupling between the coil and plasma. That capacitive coupling is defined by a voltage standing wave present on the inductive coil while powered. The higher the voltage, the greater the capacitive coupling. The cleaning efficacy at different radial and azimuthal locations on the parts varies with the value of the capacitive coupling. Also, the wear out of the plate is concentrated in one location determined by the value of the capacitive coupling.
Because of the need to keep expensive process equipment such as plasma chambers in service, it is desirable to operate the plasma chamber in a way which improves process capability, minimizes part wear, reduces time between cleans, and minimizes cleaning time. Thus, the need exists for a method and apparatus which achieves those goals.